The invention relates to two fields that can be broadly categorized as “image writing” and “image reading”. The invention's primary intended application for image writing would be as a microlithography printer for semiconductor manufacture, PCB and LCD manufacture; however this field may also include applications such as document printing, photographic reproduction, etc. Its primary intended application in the image reading field would be as a high-resolution document scanner, although it could also potentially be used for other applications, for example as a scanning microscope with camera, or as a reader for optical mass storage media, etc. The following description will focus on the photographic exposure equipment and scanning system, and more particularly, to a photolithography system and method, such as can be used in the manufacture of semiconductor integrated circuit devices, although the specification can be applied by obvious extension to other applications as well.
The present invention relates generally to in conventional photolithography systems, the photographic equipment requires a mask for imaging a pattern onto a photo resist coated subject. The subject may include, for example, a semiconductor substrate for manufacture of integrated circuits, metal substrate for etched lead frame manufacture, conductive plate for printed circuit board manufacture, or the like. A patterned mask or photo mask may include, for example, a plurality of lines, structures, or images. With conventional photolithography, the patterned masks are typically very expensive. In addition, the photomasks are characterized as requiring a very long mask purchase lead time. The long mask purchase lead time is not very helpful when a short product development cycle is desired. Further, if a particular mask design is found to require a design change in the pattern, no matter how small of a then mask modification cost and a respective lead time to implement the required change can cause serious problems in the manufacture of the desired product.
In current maskless system, there are two method which are using in actual system. One is to use a directly reduced image of a spatial light modulator (SLM) or other device on substrate surface, another is point array method which uses a microlens or multi-microlens to get a focus point array of microlens focus plane on the substrate.
Direct reduced image method is simple but the image size on the substrate is very small and cause very slow productivity.
In point array approach, each of the plurality of pixel elements is then simultaneously focused to discrete, non-contiguous portions of the subject. The subject and pixel elements are then moved (e.g., by vibrating one or both of the subject and pixel elements) and the sub-pattern is changed responsive to the movement and responsive to the pixel-mask pattern. As a result, light can be projected into the sub-pattern to create the plurality of pixel elements on the subject, and the pixel elements can be moved and altered, according to the pixel-mask pattern, to create a contiguous image on the subject. It uses a very small micolens. There are advantages to using very small microlenses for such applications. For example, the microlenses' focusing resolution may be limited by chromatic dispersion and by the size of the illumination source (if an extended source such as an arc lamp is used), but the effect of these factors can be mitigated by using small microlenses. If the microlenses are sufficiently small these factors become insignificant and focusing resolution is dominated by diffraction. If the microlens material has significant optical absorption over the operating wavelength range, it would also be advantageous to use small microlenses in order to minimize the absorption loss. However, very small microlenses cannot easily be formed without incurring significant fill factor losses. The microfabrication processes may not be able to produce accurately profiled lens surfaces if the microlens apertures are closely juxtaposed. The structure supporting the microlenses can also take up some of space between microlenses (particularly if the structural material is not optically transparent and has open light transmission channels). Furthermore, if the microlens array is integrated with electronic or micromechanical components (e.g., surface proximity sensors or microlens focus actuators), the space required to accommodate these elements can also significantly limit the lens fill factor. Point array method need to align microlens with each pixel. Any error will cause significant cross talk and noise and lower the energy efficiency. Another disadvantage is depth of focus (DOF) which affects actual system performance. The DOF of point array method is depended on microlens numerical aperture (N.A.) rather than image itself, such as an image with very rough feature size has same DOF of microlens.